460 KEPOET— 1889. 



By nsing air direct from the mains in the motor, or by heating it only 

 very slightly, the exhaust air can be, of course, so greatly reduced in 

 temperature as to be available for freezing purposes. In one Paris 

 restaurant, for instance, which I visited, I found that the exhaust was 

 carried through a brick flue into the beer cellar. In this flue the carafes 

 were set to freeze, and large moulds of block ice were also being made for 

 table use, while the air was still cold enough in passing away through the 

 beer cellar to render the use of ice for cooling quite unnecessary, even in 

 the hottest weather. The nominal function of the engine in this case 

 was the charging of batteries used in the electric lighting of the restaurant. 

 The conjoint use of power and cold is common in Paris, the power being 

 in this case generally applied in electric lighting. While in any large city 

 such as Paris it is no doubt a great point that by a compressed air 

 system the handiest possible cooling appliances can be brought everywhere 

 within reach, in tropical climates this is something rather of necessity 

 than of luxury. In such cases we might have the apparent paradox of a 

 motor worked essentially for its exhaust ; the work done would be a bye- 

 product, the cold air would be the principal thing. In such a case, if 

 there were no useful work to be done, the motor could even be made (as 

 has been suggested to me) to pump air back into the main, and thus 

 virtually to about halve its air consumption. This possibility of ' laying 

 on ' cold air in hot climates is, of course, a most important matter in 

 connection with the future of compressed air. 



Most of the compressed air in Paris is used for driving motors, but the 

 work done by these is of the most varied kind. A list which I have gives 

 the locality, use, and power of 225 installations, nearly all motors working 

 at from ^ horse-power to 50 horse-power, all driven from St. Fargeau, and 

 the great majority of them more than two miles away from it. In a 

 number of cases (as at the Eden Theatre, Theatre des Varietes, office of 

 the Petit Journal, &c.) the motor drives dynamo machines for electric 

 lighting. In the offices of the Figaro and Petit Journal large motors are 

 also used for printing, and there are many small printing establishments 

 also worked by compressed air. Among the smaller industrial purposes 

 for which the air motors are used in Paris, I find the driving of lathes for 

 metal and wood, of circular saws, shearing machines, drills, polishing 

 machines, and many others. They are used also in the workshops of 

 carpenters, joiners, and cabinet-makers, of smiths, of umbrella-makers, of 

 collar-makers, of bookbinders, and naturally in a great many places where 

 sewing machines are used, both by dressmakers, tailors, and shoemakers, 

 and from the smallest to the largest scale. They find application also in 

 all sorts of industrial woi'k, with confectioners, coffee roasters, colour 

 grinders, billiard-ball makers, in many departments of textile industry and 

 other matters too numerous to mention. 



Table.- — Summary of Efficiencies of Compressed Air Transmission at Paris, 

 1889, ietiveen the Central Station at St. Fargeau and a 10 Jiorse-power 

 •motor working ivith pressure reduced to 4^ atmospheres. 



(The figures below correspond to mean results of two experiments cold and two 



heated.) 

 1 indicated horse-power at central station gives 0'84:5 EfiSciency of main engines, 

 indicated horse-power in compressors, and corre- 0'845. 



sponds to the compression of 348 cubic feet of air 

 per hour from atmospheric pressure to 6 atmospheres 

 absolute. (The weight of this air is about 25 lbs.) 



